Clay stabilization in sub-surface formations

ABSTRACT

Compositions and methods of using same for clay stabilization in sub-surface formation are provided. The compositions comprise an aqueous solution of a polymer such as poly(dimethylaminoethylmethacrylate methyl chloride quaternary salt). The present invention can be effectively utilized to inhibit clay swelling for treating and/or pretreating down-hole formations during well stimulation.

FIELD OF THE INVENTION

The present invention generally relates to compositions and methods ofusing same for clay stabilization in sub-surface formations. Morespecifically, the present invention relates to compositions that includea polymer that is capable of inhibiting clay swelling and methods ofusing same for clay stabilization, such as in oil and gas welltreatment.

BACKGROUND OF THE INVENTION

Hydraulic fracturing has been utilized for many years to stimulate theproduction of oil, gas or other formation fluids from subterraneanformations. In hydraulic fracturing, a suitable fluid is introduced intothe down-hole formation by way of a well bore under conditions of flowrate and pressure which are at least sufficient to create or extend afracture into a desired portion of the formation. Various fluids havebeen utilized in hydraulic fracturing. Most fluids utilized today,however, are aqueous-based liquids.

The presence of clay in oil and gas producing formations poses a problemfor production from wells completed in such formations. Ordinarily, suchclays are inert in the formation and do not disrupt the flow ofhydrocarbons. When disturbed, however, by aqueous-based fluids used inwell stimulation for example, clay particles can swell and reduceformation permeability.

Clay swelling problems in the past have been addressed by preflushingwith slugs of salt-containing water and using inorganic salts in theaqueous stimulation fluid. Quite often the salt of choice has heretoforebeen potassium chloride (KCl) which converts the clay to a lessswellable form by cationic exchange with Na³⁰ ions present on the claysurfaces. Other salts include calcium chloride, ammonium chloride andthe like, typically dissolved in an aqueous preflush and/or in theaqueous stimulation fluid used for the formation treatment.

Clays dispersed throughout oil-producing formations may be described asstacked platelets with a net positive charge associated with the fourshort dimensional sides and a net negative charge associated with thetwo long dimensional faces. It is generally believed that the concept ofsurface charge may be used to understand the mechanisms involved inswelling inhibition. When the large negatively charged face or surfaceis exposed to an aqueous solution, it attracts cations from thesolution. In order to inhibit the swelling phenomenon, minimization ofthe hydratable surface area of the clay is necessary. One way that thismay be accomplished is by flocculating and decreasing the surface chargedensity, or by increasing the ionic strength of the aqueous phase, orboth. By allowing cations with small charge-to-surface-area ratios toassociate with the particle, the effective strength of the negativelycharged, double-face platelet layer surfaces will be diminished,allowing greater platelet-platelet interaction. Increasing the ionicstrength of the solutions will also have the same effect.

In the case of potassium chloride, it is generally believed that thepotential for clay swelling is shunted via a cation exchange ofpotassium ions for the more hydration-enticing native cations, such assodium. It has been found that K+ is much better at creatingelectrostatic links between the negatively charged faces of the stackedclay platelets than the abundant Na+, thus allowing less osmoticmigration of water to occur between the platelets. While a lowerconcentration of K+ ions relative to Na+ ions is needed to flocculateclays, NH₄+ ions have been shown to be even better or equal to K+ ionsin creating electrostatic links and reducing osmotic migration of water.

While salts may be effective in protecting the formation, severalproblems are generally associated with use of same. For example, theamount of material needed for preparing an effective fluid may be veryhigh, and it is often difficult to dissolve such solid components in thetreating fluids in the quantities required. In environmentally sensitiveareas, there may be limits on the permissible amount of chloride. Thepresence of salts may also interact with other additive components ofthe aqueous stimulation fluid, such as, for example, viscosifyingagents, the hydration of which is inhibited by such salts. Further, theduration of the stabilizing effect thereof generally cannot be tailoredto meet the optimum duration for a given situation. Accordingly, thereis a need for a down-hole clay stabilizing composition that is moreinert to other down-hole fluid additives, lower in chloride ion andtherefore more environmentally tolerable, which has enhanced claystabilizing effectiveness compared to potassium chloride and othersimilar salts, and which may be tailored as to the duration ofstabilizing effect.

SUMMARY OF THE INVENTION

The present invention generally relates to compositions and methods ofusing same for clay stabilization in sub-surface formations, such as inoil and gas well treatment. The compositions include a polymer, such asa cationic polymer, that is capable of effectively inhibiting clayswelling in a down-hole formation, and can be used to treat and/orpretreat a sub-surface formation for well stimulation, such asfracturing, acid treating and the like. In an embodiment, the presentinvention provides a composition suitable as an additive for inhibitingclay swelling in a down-hole formation, a well stimulation fluid thatincludes such composition, and a method for stabilizing aclay-containing formation that employs such compositions as such wellstimulation fluids.

The present invention generally relates to compositions that can beeffectively utilized to stabilize clays in sub-surface formations. Thecompositions are added to the sub-surface formations in an effectiveamount such that clay swelling can be effectively inhibited. In thisregard, the present invention can be effectively utilized to treatand/or pretreat a down-hole formation for well stimulation, such asfracturing, acid treating and the like.

In an embodiment, the present invention provides a composition for claystabilization in a sub-surface formation. The composition comprises oneor more polymers selected from the group consisting ofpoly(dimethylaminoethylmethacrylate quaternary salt),poly(dimethylaminoethylacrylate quaternary salt) anddimethylaminoethylmethacrylate quaternarysalt-dimethylaminoethylacrylate quaternary salt copolymer, wherein thepolymers have a molecular weight of about 1,000 to about 100,000.

In an embodiment, the polymers have a molecular weight of about 1,000 toabout 10,000.

In an embodiment, the polymers are selected from the group consisting ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt),poly(dimethylaminoethylacrylate dimethylsulfate quaternary salt) anddimethylaminoethylmethacrylate methyl chloride quaternarysalt-dimethylaminoethylacrylate methyl chloride quaternary saltcopolymer.

In an embodiment, the composition comprises an aqueous solution ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt).

In an embodiment, the composition further comprises one or moreingredients in addition to the polymer, wherein the ingredientsincluding viscosifying agents, crosslinking agents, bactericides,breakers, ion control agents, foaming agents including a surfactant, agas stabilizers and liquefied gas stabilizers and combinations thereof.

In an embodiment, the composition is in a form selected from the groupconsisting of a solution, an emulsion and a powder.

In another embodiment, the present invention provides a stimulationfluid. The stimulation fluid comprises an aqueous solution of one ormore polymers selected from the group consisting ofpoly(dimethylaminoethylmethacrylate quaternary salt),poly(dimethylaminoethylacrylate quaternary salt) anddimethylaminoethylmethacrylate quaternarysalt-dimethylaminoethylacrylate quaternary salt copolymer, wherein thepolymers have a molecular weight of about 1,000 to about 100,000.

In an embodiment, the stimulation fluid comprises an aqueous solution ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt).

In an embodiment, the stimulation fluid comprises up to about fourgallons of the poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt) solution per 1,000 gallons of stimulation fluid.

In an embodiment, the stimulation fluid of comprises about one to abouttwo gallons of the poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt) solution per 1,000 gallons of stimulation fluid.

In an embodiment, the stimulation fluid further comprises one or morecomponents such as viscosifying agents, crosslinking agents,bactericides, breakers, ion control agents, foaming agents including asurfactant, gas stabilizers and liquefied gas stabilizers, combinationsthereof and the like.

In yet another embodiment, the present invention provides a method ofstabilizing a clay-containing formation during a sub-surface wellstimulation process. The method includes

-   -   (i) providing a stimulation fluid comprising an aqueous solution        of one or more polymers selected from the group consisting of        poly(dimethylaminoethylmethacrylate quaternary salt),        poly(dimethylaminoethylacrylate quaternary salt) and        dimethylaminoethylmethacrylate quaternary        salt-dimethylaminoethylacrylate quaternary salt copolymer,        wherein the polymers have a molecular weight of about 1,000 to        about 100,000; and    -   (ii) contacting the sub-surface with the stimulation fluid.

In an embodiment, the stimulation fluid comprises an aqueous solution ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt).

In an embodiment, the stimulation fluid of comprises up to about fourgallons of the poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt) solution per 1,000 gallons of stimulation fluid.

In an embodiment, the stimulation fluid comprises about one to about twogallons of the poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt) solution per 1,000 gallons of stimulation fluid.

In an embodiment, the stimulation fluid further includes one or morecomponents such as viscosifying agents, crosslinking agents,bactericides, breakers, ion control agents, foaming agents including asurfactant, gas stabilizers and liquefied gas stabilizers andcombinations thereof.

An advantage of the present invention is to provide improvedcompositions for clay stabilization.

Another advantage of the present invention is to provide improved claystabilizers that can be utilized in stimulation fluids.

Yet another advantage of the present invention provides improvedcompositions that include a low molecular weight polymer for effectiveclay stabilization without addition of a salt or the like.

Yet still another advantage of the present invention provides improvedstimulation fluids and methods of using same to provide claystabilization in a sub-surface formation.

Additional features and advantages of the present invention aredescribed in and will be apparent from the following DetailedDescription of the Presently Preferred Embodiments.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention generally relates to compositions and methods ofusing same for clay stabilization in sub-surface formations, such as inoil and gas well treatment. The compositions include a polymer, such asa cationic polymer, that is capable of effectively inhibiting clayswelling in a down-hole formation, and can be used to treat and/orpretreat a sub-surface formation for well stimulation, such asfracturing, acid treating and the like. In an embodiment, the presentinvention provides a composition suitable as an additive for inhibitingclay swelling in a down-hole formation, a well stimulation fluid thatincludes such composition, and a method for stabilizing aclay-containing formation that employs such compositions as such wellstimulation fluids.

Hydrocarbon producing formations typically contain some amount of clay.When exposed to water based treating fluids, these clays will absorbwater, swell and block pore space. This can reduce permeability orswell, break loose and migrate through the formation to later causedamage in another location. Temporary clay stabilizers, such as salts,can be small enough in size to move into the pore throats of theformation matrix, but the effect is only temporary. With respect to highmolecular weight polymers, they are physically too large in size toeffectively move into the pore spaces of low permeability formations andactually plate out on the formation matrix surface. The presentinvention provides a composition comprising one or more polymers whichare small enough to effectively enter the small pore throats of lowpermeability formations and further which can provide long termprotection.

Further, the present invention can provide less material handling atcomparable costs, in comparison to the use of typical inorganic salttreatments. Another general advantage of the present invention concernsthe duration of the clay stabilizing effect. At times it is desirable toavoid a stabilization of clay by the use of an organic inhibitor thatpermanently adheres to the clay particle. Such adherence may make theclay surface oil wet. An oil wet surface is undesirable when theformation is producing oil to the borehole, since the pressure needed tomove oil past an oil wet surface is greater than the pressure needed tomove oil past a water wet surface. Therefore, less oil is produced perunit time on an oil wetted surface versus a water wetted surface. Thepresent invention permits the duration of clay stabilization to betailored to given situations.

In an embodiment, the polymer compositions include polymers prepared bypolymerization of the quaternary ammonium salts ofdimethylaminoethylmethacrylate, dimethylaminoethyl acrylate and mixturesthereof. The polymers have a molecular weight that is sufficiently lowto inhibit clay swelling. For example, the molecular weight can rangefrom about 1,000 to about 100,000, preferably about 1,000 to about10,000. The composition may, but does not necessarily include a salt,such as KC₁, NH₄Cl, NaCl, TMAC and the like.

“Quaternary ammonium salts”, quaternary salt” and “quat” means the saltresulting from reaction of the tertiary nitrogen atom ofdimethylaminoethylmethacrylate, dimethylaminoethyl acrylate with aquaternizing agent or acid. Representative quaternary salts includedimethyl sulfate quaternary salts, benzyl chloride quaternary salts,methyl chloride quaternary salts, and the like. Representative acidsalts include hydrochloric acid salt, sulfuric acid salt, and the like.

Preferred polymers include dimethylaminoethylmethacrylate methylchloride quaternary salt (DMAEM-MCQ), dimethylaminoethylacrylatedimethylsulfate quaternary salt (DMAEA-MSO₄Q) anddimethylaminoethylmethacrylate-dimethylaminoethyl-acrylate copolymer(DMAEM-DMAEA). A more preferred polymer isdimethylaminoethylmethacrylate methyl chloride quaternary salt, alone orin combination with other suitable polymer materials, ingredients andthe like. Additional ingredients can include, for example, viscosifyingagents, crosslinking agents, bactericides, breakers, ion control agents,foaming agents including surfactants, gas stabilizers and liquified gasstabilizers, combinations thereof and the like. In an embodiment, thedimethylaminoethylmethacrylate methyl chloride quaternary saltcomposition is in an aqueous solution form. However, it should beappreciated that the composition of the present invention can include asolution, an emulsion, a powder and the like.

As previously discussed, the present invention relates to a stimulationfluid that includes a polymer composition in solution form as discussedabove. The polymer composition can be added to the stimulation fluid inany suitable concentration. In an embodiment, the stimulation fluidcomprises an polymer solution at a concentration of about four gallonsof the aqueous polymer composition in solution per 1,000 gallons ofstimulation fluid or less, preferably from about one gallon of theaqueous polymer composition in solution per 1,000 gallons of stimulationfluid to about two gallons of the aqueous polymer composition insolution per 1,000 gallons of stimulation fluid. The polymer compositionincludes at least one of the polymers of this invention, preferablydimethylaminoethylmeth-acrylate methyl chloride quaternary salt, aloneor in addition to other ingredients including additional otherpolyelectrolytes, copolymers thereof, and the like. In an embodiment,the stimulation fluid does not include a salt or other similar type ofclay swelling inhibition agent.

The stimulation fluid can be made in any suitable manner. In anembodiment, the stimulation fluid is preferably prepared by admixing aquantity of the clay stabilizing composition of the present inventionand a polymeric viscosifying agent with an aqueous fluid. Alternatively,the stimulation fluid may be prepared by blending together the variouscomponents, such as the cationic polyelectrolyte and the viscosifier, inthe desired proportion in any combination or order.

In an embodiment, the viscosifying agent includes a solublepolysaccharide. Representative examples pf soluble polysaccharidesinclude galactomannan gums (guar), glucomannan gums, cellulosederivatives, and the like. In an embodiment, the stimulation fluidincludes a viscosifying agent in a concentration of about 100 to about600 pounds per 1,000 gallons of the aqueous stimulation fluid.

The stimulation fluid can carry conventional suspended proppants, suchas glass beads, which are forced into the fracture or fractures to keepthe broken formation from closing completely once the pressure isreleased. However, the use of such proppants is not necessary to achievethe clay stabilization obtained by the present simulation fluid.

The stimulation fluid also can include a crosslinking agent for theviscosifying agent as well as other suitable additives. For example, thefluid can contain bactericides, breakers, iron control agents, foamingagents such as surfactants, gases or liquefied gases stabilizers, andthe like. The preparation of such fluids and the various additives arewell known in the art. The selection of the particular stimulating fluidconstituents and amounts thereof such as the viscosifying agent,crosslinking agent, breakers, stabilizers can be made in any suitablemanner.

The clay swelling inhibitor composition, or components thereof, areadmixed with an aqueous stimulation fluid in an amount sufficient tosubstantially stabilize the formation against permeability damage as theresult of contact with the aqueous stimulation fluid. In this regard,the clay swelling inhibitor composition can be made in a liquid state,in contradistinction to potassium chloride and similar salts which arecrystalline solids, and the present composition may be readily admixedwith the stimulation fluid at any time prior to contact of the fluidwith the formation. Alternatively, the present composition may beadmixed with constituents of the liquid viscosifying agent and stored asa ready-to-use stimulation fluid additive concentrate.

The clay swelling inhibitor additive is effective in treating a downhole formation when transported in a carrier fluid, such as awell-stimulation fluid having either an acid, alkaline or neutral pH.The stimulation fluid of the present invention can have a pH in therange of from about 0 to about 11 without any significant negativeeffects upon the activity thereof, although preferably the pH of thestimulation fluid is within the more moderate range of from about a pHof 0 to about a pH of 10 according to an embodiment of the presentinvention.

It should be appreciated that the present invention can be made and usedin any suitable manner, can include any suitable materials and bemodified in any suitable manner. Examples of various and suitablematerials, such as stimulation fluid additives, of the present inventioncan be found in U.S. Pat. Nos. 5,342,530; 5,152,906; and 5,099,923, thedisclosures of which are herein incorporated by reference.

An illustrative example of the present invention according to anembodiment is provided below without limitation. TABLE I Synthesis ofPolydimethylaminoethylmethacrylate-methyl chloride quaternary saltSolution (DMAEM-MCQ Solution) Wt % in Step # DMAEM-MCQ Solution grams(g) Formulation 1 Dimethylaminoethylmethacrylate 316.8 31.68 methylchloride quaternary salt (75 wt % aq) (DMAEM-MCQ) 2 D.I. Water 318.9231.89 3 Sodium Hypophosphite hydrate 3.56 0.356 (solid) 4 Vazo 67 0.640.064 5 Methanol 193 19.3 6 D.I. Water 167.08 16.71 7 Total grams 1,000100.0

A DMAEM-MCQ Solution was made according to an embodiment of the presentinvention as shown in Table I above and further described in detailbelow. To a 2-liter 4-neck round bottom flask equipped with an overheadstirrer, a nitrogen (N₂) inlet tube, a Dean-Stark trap, an overheadcondenser, and a temperature regulator probe installed was addedDMAEM-MCQ, water, and sodium hypophosphite with stirring (Material steps1-3, amounts described above). Stirring of the materials was conductedat room temp, an N₂ purge was started at 500 milliliters/minute for 30minutes, and the material mix was heated to 70° C. Vazo 67 was thenadded to the mixture, stirring was continued, and the N₂ purge tube wasraised just above the surface of the liquid in the flask (to reduceentrained vapor loss). Within approximately 20 minutes, an exotherm wasnoted to 74° C. The temperature decreased to 70° C. and stirring wascontinued for approximately 8 hours.

A mass balance was then run on the product (clear, syrup). Approximately8 grams of material was lost to vaporization. This was assumed to beD.I. water and thus 8 grams of D.I. water was added to the flask andcontents stirred. At this point the product was clear, but many bubbleswere entrained. Steps 5 and 6 were then conducted where methanol and afinal water addition were carried out (see Table I above). Addition ofthese materials was performed very slowly with stirring. The productappeared hazy for a brief period and then cleared up. The viscosity,specific gravity and pH were measured for the DMAEM-MCQ Solution madeaccording to an embodiment of the present invention as described above.The following Table II provides the viscosity, specific gravity, and pHdata as measured: TABLE II Spec gravity Viscosity (cps) LV SpindleMaterial pH @ 20° C. 1, 30 rpm DMAEM-MCQ 4.42 1.0552 85.4 cps Solution(42.7 dial, 2x factor)

A number of experiments have been conducted that demonstrate thebeneficial effects of the present invention. The experiments and resultsthereof are described below according to an embodiment of the presentinvention without limitation.

The experiments were conducted to compare the clay stabilizationproperties of a. composition made pursuant to an embodiment of thepresent invention to commercially available clay stabilization products.As indicated in Table III below, three products were evaluated duringthis study, namely Products A-C. Product A is apolyepichlorohydrin-trimethylamine quaternary salt that has a molecularweight of about 1,000. This product is commercially available. Product Bis a commercially available DMAEMA-methylsulfate quaternary salt thathas a molecular weight of about 800,000. Product C is a claystabilization composition made pursuant to an embodiment of the presentinvention. More specifically, Product C includes adimethylaminoethylmethacrylate methyl chloride quaternary salt that hasa molecular weight of about 4,000.

The clay stabilization properties of each of Products A-C were evaluatedby measuring the permeability in millidarcies (md) of a BanderaSandstone core after being treated by a standard 3.5% sodium chloridebrine to establish a baseline for the test. The permeability wasmeasured initially or before addition of the product clay stabilizer.The permeability was then again measured after the core had been treatedwith a product clay stabilizer and then flushed with ten pore volumes ofdeionized (D.I.) water. Each of the product stabilizers were added atvarious dosage levels measured in “gpt” where one gpt represents onegallon of product clay stabilizer added to 1,000 gallons of treatment orcarrier fluid.

Any decrease in permeability between the before and after measurementsindicates that clay swelling has occurred. As shown in Table III below,the product clay stabilizer according to an embodiment of the presentinvention outperformed product clay stabilizers that are commerciallyavailable. TABLE III Clay Stabilizer Test Permeability Product # Before(md) Dosage (gpt) Permeability After (md) A 4.2 1 0.5 A 3.2 10 3.3 B 585 46 B 2.8 1 1.6 C 65 2 68 C 4.0 2 3.8 C 2.6 1 1.7

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A composition for clay stabilization in a sub-surface formation, thecomposition comprising one or more polymers selected from the groupconsisting of poly(dimethylaminoethylmethacrylate quaternary salt),poly(dimethylaminoethylacrylate quaternary salt) anddimethylaminoethylmethacrylate quaternarysalt-dimethylaminoethylacrylate quaternary salt copolymer, wherein thepolymers have a molecular weight of about 1,000 to about 100,000.
 2. Thecomposition of claim 1 wherein the polymers have a molecular weight ofabout 1,000 to about 10,000.
 3. The composition of claim 2 wherein thepolymers are selected from the group consisting ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt),poly(dimethylaminoethylacrylate dimethylsulfate quaternary salt) anddimethylaminoethylmethacrylate methyl chloride quaternarysalt-dimethylaminoethylacrylate methyl chloride quaternary saltcopolymer.
 4. The composition of claim 1 comprising an aqueous solutionof poly(dimethylaminoethylmethacrylate methyl chloride quaternary salt).5. The composition of claim 1 further comprising one or more ingredientsin addition to the polymer, wherein the ingredients are selected fromthe group consisting of viscosifying agents, crosslinking agents,bactericides, breakers, ion control agents, foaming agents, a gasstabilizers and liquefied gas stabilizers and combinations thereof. 6.The composition of claim 1 wherein the composition is in a form selectedfrom the group consisting of a solution, an emulsion and a powder.
 7. Astimulation fluid comprising an aqueous solution of one or more polymersselected from the group consisting ofpoly(dimethylaminoethylmethacrylate quaternary salt),poly(dimethylaminoethylacrylate quaternary salt) anddimethylaminoethylmethacrylate quaternarysalt-dimethylaminoethylacrylate quaternary salt copolymer, wherein thepolymers have a molecular weight of about 1,000 to about 10,000.
 8. Thestimulation fluid of claim 7 wherein the polymers have a molecularweight of about 1,000 to about 10,000.
 9. The stimulation fluid of claim8 wherein the polymers are selected from the group consisting ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt),poly(dimethylaminoethylacrylate dimethylsulfate quaternary salt) anddimethylaminoethylmethacrylate methyl chloride quaternarysalt-dimethylaminoethylacrylate methyl chloride quaternary saltcopolymer.
 10. The stimulation fluid of claim 7 comprising an aqueoussolution of poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt).
 11. The stimulation fluid of claim 10 comprising up toabout four gallons of the poly(dimethylaminoethylmethacrylate methylchloride quaternary salt) solution per 1,000 gallons of stimulationfluid.
 12. The stimulation fluid of claim 10 comprising about one toabout two gallons of the poly(dimethylaminoethylmethacrylate methylchloride quaternary salt) solution per 1,000 gallons of stimulationfluid.
 13. The stimulation fluid of claim 7 further comprising one ormore ingredients selected from the group consisting of viscosifyingagents, crosslinking agents, bactericides, breakers, ion control agents,foaming agents, gas stabilizers and liquefied gas stabilizers andcombinations thereof.
 14. A method of stabilizing a clay-containingformation during a sub-surface well stimulation process, the methodcomprising the steps of: (i) providing a stimulation fluid comprising anaqueous solution of one or more polymers selected from the groupconsisting of poly(dimethylaminoethylmethacrylate quaternary salt),poly(dimethylaminoethylacrylate quaternary salt) anddimethylaminoethylmethacrylate quaternarysalt-dimethylaminoethylacrylate quaternary salt copolymer, wherein thepolymers have a molecular of about 1,000 to about 100,000; and (ii)contacting the sub-surface with the stimulation fluid.
 15. The method ofclaim 14 wherein the polymers have a molecular weight of about 1,000 toabout 10,000.
 16. The method of claim 15 wherein the polymers areselected from the group consisting ofpoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt),poly(dimethylaminoethylacrylate dimethylsulfate quaternary salt) anddimethylaminoethylmethacrylate methyl chloride quaternarysalt-dimethylaminoethylacrylate dimethyl methyl chloride quaternary saltcopolymer.
 17. The method of claim 16 wherein the stimulation fluidcomprises an aqueous solution of poly(dimethylaminoethylmethacrylatemethyl chloride quaternary salt).
 18. The method of claim 16 wherein thestimulation fluid of comprises up to about four gallons of thepoly(dimethylaminoethylmethacrylate methyl chloride quaternary salt)solution per 1,000 gallons of stimulation fluid.
 19. The method of claim16 wherein the stimulation fluid comprises about one to about twogallons of the poly(dimethylaminoethylmethacrylate methyl chloridequaternary salt) solution per 1,000 gallons of stimulation fluid. 20.The method of claim 14 wherein the stimulation fluid further comprisesone or more components selected from the group consisting ofviscosifying agents, crosslinking agents, bactericides, breakers, ioncontrol agents, foaming agents, gas stabilizers and liquefied gasstabilizers and combinations thereof.